Helmet-Mounted Displays: - USAARL - The - U.S. Army

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Optical Performance 129 Figure 5.9. Representative model output for a CRT display using P28 phosphor (70-msec persistence) and having a vertical frame rate of 33 msec (Rash and Becher,1983). msec is typical. This value is defined by the pixel access time (relatively short, ~65 �sec), crystal’s response speed, and other LCD physical properties such as the dependence of cell capacitance on drive voltage and temperature (Bitzakidis, 1994; Leroux, 1989). In a similar fashion to CRT phosphor response, the slow transition between luminance values will degrade modulation transfer in dynamic images on AMLCDs. Consider the example of a black vertical bar moving across a white background where the luminance changes are completed after addressing the pixels twice (Bitzakidis, 1994). The display pixels can be categorized as: a) Background pixels, which remain white for two fields. b) Overlap-area pixels between the presentations of the bar at different fields, which remain black for two fields. c) Pixels which change from white to black (the leading edge of the bar). d) Pixels which change from black to white (the trailing edge of the bar).
130 Clarence E. Rash and William E. McLean The leading edge of the bar will appear dark grey, since the transition Figure 5.10. MTF curves for P1 phosphor (Beasley et al., 1995). from white to black will be incomplete. The area behind the trailing edge suffers also. It will be a light grey due to the incomplete transition from black to white. The overall effect is that of a low-pass filter. Motion blur will result with a loss of high frequency detail. The magnitude of the effect increases with speed. Rabin and Wiley (1995) compared visual performance between CRT and liquid crystal displays for high rates of image presentations and found a significant difference, which was attributed to the display response speed. The study involved a target detection task for various horizontal target velocities presented on the IHADSS (using a P43 phosphor image source) and an AMLCD HMD developed by Honeywell, Inc., Minneapolis, Minnesota. Target recognition (contrast sensitivity) was found to be degraded for the AMLCD HMD for the three highest velocities tested (4.4- 17.6 deg/sec). In conclusion, the dynamic response of a display and its interaction with other imaging system components is a critical area of concern. Therefore, it is necessary to be able to measure the dynamic MTF of such systems. Current wisdom is that pixel persistence (10%) values greater
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Helmet-Mounted Displays: Design Iss
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The views, opinions, and/or finding
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vi Contents 4. Visual Coupling Clar
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viii Contents References ..........
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x Ben T. Mozo, Research Physicist U
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xii Foreword began its phenomenal e
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xiv Preface Acknowledgments The aut
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Introductory Overview 1 Clarence E.
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Introductory Overview 5 Figure 1.2.
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Introductory Overview 7 The trend f
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Introductory Overview 9
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Introductory Overview 11 aviator to
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Introductory Overview 13 1970's. Ta
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Introductory Overview 15 Image sour
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Introductory Overview 17
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Table 1.3. HMD performance figures-
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Introductory Overview 21 direct vie
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Introductory Overview 23 Figure 1.9
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Introductory Overview 25 Figure 1.1
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Introductory Overview 27 Ercoline,
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Introductory Overview 29 II, Procee
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Introductory Overview 31 Armstrong
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34 Clarence E. Rash, Melissa H. Led
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40 Liquid crystal Clarence E. Rash,
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Optical Designs 3 William E. McLean
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Optical Designs 57 and plotted in l
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Optical Designs 59 phosphors, (b) u
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Optical Designs 61 optics. Examples
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Optical Designs 63
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prism combiner. Optical Designs 65
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Figure 3.2. (continued) Optical Des
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Optical Designs 69
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Optical Designs 71 Figure 3.4. Comp
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Optical Designs 73 Figure 3.6. Opti
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Optical Designs 75 Figure 3.8. Refl
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Optical Designs 77 Figure 3.9. Ray
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Optical Designs 79 incidence and re
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Page 116: DESIGN ISSUES PART TWO
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Page 121 and 122: 104 Contrast Clarence E. Rash and W
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Visual Performance 179 individuals
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Visual Performance 181 0 to -5.25 d
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Visual Performance 183 Report No. 9
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Biodynamics 7 B. Joseph McEntire He
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Biodynamics 187 behavior of this de
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Figure 7.2. Head anatomical coordin
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Biodynamics 191
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Biodynamics 193 al., 1972), and man
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Biodynamics 195 Figure 7.5. Vertica
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Biodynamics 197 disability and fata
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Biodynamics 199 been fabricated int
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Biodynamics 201 Ty pic al acc ele r
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Biodynamics 203 exceed the mechanic
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Biodynamics 205 complexity and comp
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Type Reference helmet Foam in place
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Biodynamics 209 the fitting problem
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Biodynamics 211 adjustment buckle,
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Biodynamics 213 down. The helmet ma
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Biodynamics 215 Desert Shield/Deser
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Biodynamics 217 Donelson, S. M., an
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219 Fort Rucker, AL: U.S. Army Aero
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220 Ben T. Mozo Figure 8.1. Noise l
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222 Ben T. Mozo available in the ne
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224 Ben T. Mozo Protectors”(ANSI,
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226 Ben T. Mozo language. Tests of
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228 Ben T. Mozo Figure 8.6. Speech
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230 Ben T. Mozo the communications
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232 Ben T. Mozo Item Mass (grams) C
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Ribera, J. E., and Mozo, B. T. Unda
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236 Joseph R. Licina operational us
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238 Joseph R. Licina Standard MIL-S
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240 Joseph R. Licina On electro-opt
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242 Joseph R. Licina For HMDs with
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244 Joseph R. Licina 1994b) that wi
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246 Joseph R. Licina Table 9.2. Hea
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248 Joseph R. Licina provided a 93.
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250 Joseph R. Licina and buckles, a
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252 Joseph R. Licina authorized to
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254 Joseph R. Licina a nuclear flas
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256 Joseph R. Licina requirements:
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HMD PERFORMANCE ASSESSMENT PART THR
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262 Clarence E. Rash, John C. Mora,
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Glossary 11
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270 making stereoposis possible. Bi
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272 John C. Mora and M elissa H. Le
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NOTES ON CONTRIBUTORS Melissa H. Le
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Notes on Contributors 281 Research
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284 Index Breakaway force (see Fran
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286 Index movement, 55, 80, 84, 90,
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288 Index 198, 204, 205, 208, 210,
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290 Index Microphone, 15, 186, 224,
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292 Index Speech intelligibility (S
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